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During the last ice age (and others before it) temperatures across the Northern Hemisphere would abruptly swing up and down by a hefty 3 – 6°C every 1,500 years or so. A new study using isotopes on the sea floor rather provocatively suggests that the Atlantic ocean circulation was to blame. Apparently it slowed almost to halt, and before the surface water cooled. It seems that when the Atlantic currents slow too far they stop bringing warmer water north from the equator and Southern Hemisphere, and thus the north ices over. During these super-cold periods the ice sheets spread down and cover much of North America, (and real estate in Australia costs a motza). Massive icebergs break off and drift, but apparently things took a lot longer to get cold in the Southern Hemisphere, and the north and south possibly got a bit out of whack cooling and warming in opposite phases. The researcher used the word “bipolar”.

The $64 trillion dollar question is if ocean currents cause climate change, what causes the ocean currents? The researchers don’t know. (Seems kind of important). Things stabilized out in the last 10,000 warm years. It looks like the wild swings don’t occur [...]

Is this the way the backdown plays out? The endless warming becomes cooling, and man-made change becomes natural cycles one paper at a time? The press releases still talk of “change”! No mention that natural cycles could have been the cause of past warming, and that skeptics have been saying this for years.

Figure 3 | Sea-level circulation index, the NAO and the AMO on multidecadaltimescales. Shown are the accumulated sea-level index (blue), which isrepresentative of subpolar heat content evolution, the accumulated NAO (red,dashed) and the AMO (black). The heat content proxy and the accumulatedNAO have been normalized. All timeseries have been 7-year low-pass filtered.The accumulated sea-level index and accumulated NAO have been detrended.

This Nature paper will be tricky to feed into the “Panic Now!” scenario. It’s still climate change, but it’s a half a degree of cooling that might be headed your way if you live around the northern Atlantic.

UPDATE: A quick summary of the paper. McCarthy et al created a circulation index (blue line, fig 3) which appears to lead the AMO (Atlantic Multidecadal Oscillation, black line) by two years. The sea level index is generated by comparing sea levels north and south of [...]

Who would have thought that if you knew the air pressure in Darwin and Tahiti in June, you could figure out that the start of 2011 might be a Stalingrad Winter up North and a cooler wetter summer down south (Not that people in Sydney feel all that cool right now). But the air pressure ratios are reported as the SOI (Southern Oscillation Index) and it’s the handiest thing if you like predicting global temperatures 7 months ahead. Look at that correlation.

Since June last year Bryan Leyland has been using the simple connection described by Carter, De Freitas, and McLean in 2009 to predict up and coming temperatures.

So far, for what it’s worth, he’s right on track.

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Such is the power of the stored pool of cold that is the bottom three-quarters of the Pacific Ocean. And when you look at how vast the Southern Pacific ocean is, is it any wonder it has such an influence? All that heat capacity…